The invention relates to a radar range measuring device with a transmitter directing a frequency-modulated continuous radio frequency signal via an antenna onto an object placed at the range to be determined; with a mixing stage which combines with one another, on the one hand, signals tapped from the transmitter, and, on the other hand, echo signals received from the target object via the antenna and/or another antenna; with a frequency analysis device for frequency analysis of the mixing result; and with a display device to display the range corresponding to a target-object-specific frequency of the mixing result.
In known radar range measuring devices with sawtooth frequency modulation, the frequency swing (difference between upper frequency limit and lowerfrequency limit) of the frequency modulation of the transmit signal is used to determine the range resolution, which is related to the frequency swing via the following equation:
range resolution=speed of light/2*frequency swing
For example, if a range resolution of 10 cm is required, then for known radar range measuring devices operating on the FMCW principle it is necessary to provide a frequency swing of 1.5 GHz. But if a smaller frequency swing has to be selected, e.g., because of bandwidth restrictions imposed by licensing regulations of the postal administration, then the range resolution is worsened correspondingly toward larger values.
In EP-A-0647957 a method is described which provides a large number of measuring cycles in order to improve the measuring accuracy and/or the range resolution.
The problem to be solved by the invention is to configure a radar range measuring device of the general type briefly described here in above so that a high range resolution is achieved when the frequency swing of the frequency modulation of the transmit signal is limited, without any need to perform a large number of measuring cycles.
That problem is solved according to the invention by the characterizing features of patent claim 1 hereinbelow.
Advantageous configurations and developments are the subject matter of the patent claims subordinated to claim 1, to whose content express reference is made here without repeating their wording at this point.
But it should be noted that for full exploitation of the advantages achieved by the invention it is important that the frequency modulation of the frequency of the oscillation radiated toward the target object be performed with utmost precision, preferably a linear or sawtooth frequency modulation being selected.
According to a very suitable embodiment of a radar range measuring device of the type indicated here, that modulation is performed by adjustment of an oscillator to specified frequencies in a highly precise manner within each period corresponding to the sampling clock of the signal processing, those frequencies having values which are located with corresponding accuracy on the desired frequency characteristic versus time, i.e., exactly on a straight line in the case of sawtooth modulation.
Another important improvement of a radar range measuring device of the type indicated here is that the phase position of the determined target-object-specific frequency is obtained and evaluated as the result of a direct Fourier transformation, i.e., in the sense that, to determine the range being measured, one not only counts out the full periods of the target-object-specific frequency of the mixing result but rather one supplements the corresponding multiple of the wavelength by the fraction of the wavelength corresponding to the phase angle.